The long-term objective of this research is to reduce the incidence of infection with human immunodeficiency virus type 1 (HIV) in industrialized countries by developing methods to identify and treat high-risk individuals whose response to HIV testing and counseling is hindered by psychopathology. The project's specific aims are (1) to describe the distribution of psychopathologies among persons undergoing HIV testing and counseling, and (2) to test the hypotheses that high-risk, HIV-seronegative persons with mild-to-moderate depression will be more likely to adopt protective behavior changes when provided with pharmacotherapy for their depression than when treated with placebo. The study design to achieve specific aim 2 will be a randomized, double-blinded clinical trial of bupropion hydrochloride versus placebo administered for a total of 7 months. The study population will be initially high-risk, HIV-seronegative men who have sex with men (MSM). Individuals who are ineligible or decline entry into the clinical trial will be entered into an observational study. The primary outcome measure of the clinical trial will be self-reported numbers of partners in unprotected receptive anal intercourse. Secondary outcomes will be substances used and frequency of substance use by self-report and toxicology; (c) new infections with sexually transmitted infections including gonorrhea, syphilis, Kaposi's sarcoma-associated herpesvirus, and hepatitis C virus (HCV) and HIV; and (d) measures of psychological factors that have been shown to be, or are thought to be, associated with HIV incidence rates, including measures of self-efficacy, self-esteem, stage of change, and depression. Enrollment data from the observational study will be combined with enrollment data from the clinical trial to provide a description of the distribution of psychopathologies and substance abuse among high-risk MSM. Longitudinal data form the observational study will be used to assess the associations of psychopathologies, substances used and frequency of substance use with adverse outcomes.